As satellite broadcasting spreads widely these years, various sorts of antennas for reception of satellite broadcasting waves designed for mounting on vehicles have been studied. References of such typical antennas and antennas related thereto include:
(1) Furukawa et al.: "Beam Tilt Type Planar Antenna using Waveguide of Single-Layer Structure for Receiving Broadcast by Satellite", Technical Report of IEICE (The Institute of Electronics, Information and Communication Engineers), AP88-40, July 1988. PA1 (2) Ohmaru: "Mobile reception apparatus for broadcast by satellite", Broadcasting Technology, vol. 43, no. 9, pp. 119-123, September 1990. PA1 (3) Kuramoto et al.: "Antenna System for Mobile DBS Reception", Proceedings of the General Meeting of IEICE in Spring, 1991, B-59, March 1991. PA1 (4) Nishikawa: Mobile Antenna System for Receiving Broadcast by Satellite, Toyoda Chuo Research R&D Review, vol. 27, no. 1, p65, March 1992. PA1 (5) Hirokawa et al.: "Design of Slotted Leaky Waveguide Array Antenna", Technical Report of IEICE, AP92-37, 1992-5. PA1 (6) Nakano et al.: "Curl Antenna (III)- Beam Tilt", Proceedings of the General Meeting of IEICE in Spring, B-45, March 1993. PA1 (7) Takano et al.: "System for Mobile BS Reception on Small Passenger Car", Proceedings of the General Meeting of IEICE in Spring, 1993, B-46, March 1993. PA1 (8) Fujita et al.: "Study of System for Mobile BS Reception on Airplane", Proceedings of the General Meeting of IEICE in Spring, 1993, B-47, March 1993. PA1 (9) Shibata et al.: "Characteristics of Radial Line Microstrip Array Antenna having Large Tilt Angle", Proceedings of the General Meeting of IEICE in Spring, 1993, B-54, March 1993. PA1 (10) J. Hirokawa et al.: "Waveguide .pi.-Junction with an Inductive Post", IEICE Trans. Electron, vol. 75, no. 3, pp. 348-351, March 1992. PA1 (11) N. Marcuvits: "Waveguide Handbook", IEE Electromagnetic Wave Series 21, Peter Peregrins Ltd., Chaps. 5&6,1986. PA1 (12) J. Hirokawa et al.: "A Single-Layer Multiple-Way Power Divider for a Planar Slotted Waveguide Array", IEICE Trans. Commun., vol. 75, no. 8, pp. 781-787, August 1992 PA1 (13) Mizuno et al.: "E-Plane Curve 4-Power Distributor", Proceedings of the General Meeting of IEICE in Spring, 1989, C-788, March 1989. PA1 (14) J. Hirokawa et al.: "An Analysis of a waveguide T Junction with an Inductive Post", IEEE Trans. Microwave Theory Tech., vol. 39, no. 3, pp. 563-566, March 1991. PA1 (15) J. Hirokawa et al.: "Matching Slot Pair for a Circularly-Polarized Slotted Waveguide Array", IEE Proc., vol. 137, pt. H, no. 6, pp. 367-371, December 1990. PA1 (16) Kiyohara et al.: "Design of a crossed Slot Array Antenna on a Leaky Waveguide", Technical Report of IEICE, AP91-75, September 1991. PA1 (17) J. Hirokawa, M. Ando and N. Goto: "Analysis of Slot Coupling in a Radial Line Slot Antenna for DBS Reception" IEE Proc., vol. 137, pt. H, no. 5, pp. 249-254, October 1990. PA1 (18) J. Hirokawa et al.; "Design of a Crossed Slot Array Antenna on a Leaky Waveguide", Technical Report of IEICE A.P 92-37, EMCJ92-20, May 22, 1992.
With respect to such an antenna for reception of broadcast by satellite, since the antenna is to be mounted on a roof or the like of the automotive vehicle running on a road on which heights of the cars are legally restricted, one of important technical problems of such an antenna is to reduce the antenna height. Further, since the signal reception antenna is to be on a limited area on the roof of the car, another important technical problem is to minimize the antenna mounting area. In order to reduce the mounting height of the signal reception antenna, such a planar antenna of a structure that has a beam tilt angle and is designed to be mounted on the roof of the car is preferably considered.
In the case of an antenna for reception of satellite broadcast designed for mounting on a car, for the purpose of enabling the signal reception antenna to catch at all times the direction of the broadcasting satellite which varies with time as the car moves, the antenna is required to have a tracking mechanism for controlling the azimuth and elevation angles of the antenna. The tracking mechanism, however, constitutes a considerable part of the whole antenna manufacturing cost and also increases the mounting height and area of the antenna. Thus, it is important to eliminate or minimize such a drawback. Since the azimuth varies throughout 360 degrees with the movement of the car, it becomes necessary to realize the tracking of the azimuth direction by a mechanical rotary mechanism. Meanwhile, since the elevation angle is caused by a latitude range (about 20 degrees, for example, for vehicles in Japan) or by a slope of road relative to horizon level, that is, by a road slope within about .+-.5 degrees, the range of elevation change is relatively limited. For this reason, when the main beam width of the antenna in the elevation direction is previously set wider than the above values, a non-tracking system not for performing the mechanical tracking in the elevational direction can be employed to result in economy of the signal reception system, as a whole.
Referring to the aforementioned documents (2), (4), (7) and (8), it is difficult for a planar antenna using microstrips to realize more than 30 degrees of beam tilt angle, so that, when it is desired to obtain a beam tilt angle of about 50 degrees, the antenna must be installed to be inclined by about 20 degrees from the horizontal plane. In this case, the height of the inclined antenna determines the height of the entire signal reception system, which disadvantageously involves increase of the mounted height of the signal reception system when mounted on a vehicle. In order to reduce the antenna height, the antenna is divided into a plurality of subarrays.
Referring to the aforementioned documents (6) and (9), a planar antenna using radial waveguide path has a circular shape. For this reason, when it is desired for the planar antenna to be rotated about its center for tracking in the azimuth direction, a useless space can be removed and thus its mounting area can be decreased. In the case of the planar antenna using radial waveguide path, however, in order to obtain a large beam tilt angle while suppressing its side lobe, a substrate must be made of material having a high dielectric constant and antenna elements must be arranged in a close positional relationship. It seems very difficult to manufacture such an antenna in a mass production at the current technical level. In addition, because of the circular antenna, its beam width has a low degree of design flexibility.
Disclosed in the aforementioned documents (1), (3) and (5) is a slotted leaky waveguide array antenna which comprises a plurality of radiation waveguides provided therein with a plurality of slots along their electromagnetic-wave propagating direction and arrayed adjacent to each other in the same direction as the wave propagating direction and also comprises a feed waveguide for composing a wave of electromagnetic waves received by the respective radiation plate waveguides and transmitting the wave to a converter. This slotted leaky waveguide array antenna is considered to have an advantage that the beam width and antenna gain can be adjusted substantially independently of each other, depending on the number of such slots made in the respective radiation waveguides and the number of such radiation waveguides. Further, since the antenna disclosed in the above documents (1) and (5) is of a single-layer structure type, it is advantageous that a slot plate having respective slot patterns formed by etching is mounted on the waveguides of a groove structure by laser fusing, whereby an inexpensive and simple antenna can be manufactured.
The above prior art slotted leaky waveguide array antenna has many advantages including the above. However, in this antenna, as described in the document (5), a coupling part of the feed waveguides to the converter is provided at one end of the antenna. For this reason, when it is desired for the antenna to be rotated about its center for tracking in the azimuth direction, the antenna must have such a structure that the converter is fixedly mounted to the rear side of the antenna to be rotated together with the antenna. This requires the rotary mechanism to have a large load, which results in that a response performance is reduced, the vibration and shock caused by the rotation are applied to the converter, whereby the electronic circuit of the converter may be deteriorated.